1. Field of the Invention
The invention relates to a process for the production of metal salts of trifluoromethane sulphonic acid by reacting trifluoromethane sulphonic acid with a metal alcoholate and their use as esterification catalyst and/or transesterification catalyst for the production of hydroxycarboxylic acid esters.
2. Description of Prior Art
Trifluoromethane sulphonic acid (CF3SO3H) is one of the strongest organic acids. Its protonation power is stronger than that of sulphuric acid. Its metal salts, i.e. metal perfluoromethane sulphonates, also called metal triflates, are available as solids or in solution.
The most frequent fields of application of metal compounds of trifluoromethane sulphonic acid are their use as catalyst in the polymerisation of aromatic alkenes, of aromatic monomers, in electrophilic polymerisation of 1,3-pentadiene, the cationic ring opening polymerisation of tetrahydrofuran, in the Michael reaction of O-silylated ketene acetals with alpha,beta-unsaturated esters. Further fields of application are aldol and Friedel-Crafts reactions.
From U.S. Pat. No. 4,219,540, the production of metal salts of trifluoromethane sulphonic acid and their use in antiperspirants is known. The aluminium salt of trifluoromethane sulphonic acid is produced by adding trifluoromethane sulphonic acid at room temperature to an aqueous suspension of barium carbonate and stirring the mixture, filtering it and removing water from it at reduced pressure and elevated temperature and drying it.
The barium trifluoromethane sulphonate thus obtained is again dissolved in water, stirred and aluminium sulphate dissolved in water is added at room temperature. After heating, filtration is carried out and the filtrate is decolorised with carbon, filtered once more and water is driven off at reduced pressure and elevated temperature, and it is dried. In a similar manner, the corresponding triflates have been produced for the rare earth metals Ce, La and the Nd—Pr alloy didymium [neodymium-praeseodymium-alloy].
A disadvantage is the complicated recovery of the metal triflate and the low yield with respect to the trifluoromethane sulphonic acid used.